1. Field of the Invention
The present invention generally relates to optical recording media, and more particularly, to a ROM-RAM recording medium that includes: a ROM portion having an optically transparent substrate on which main information is recorded by physical change such as an irregularity formed as, for example, pits; and a RAM portion formed on the ROM portion as a recording layer that allows writing of main information at least once, wherein a sub-code region for recording sub-information is provided in the ROM portion, and to a storage device for such a ROM-RAM recording medium.
2. Description of the Related Art
Conventional media having both ROM (Read-Only Memory) part and RAM (Random Access Memory) part therein include, for example, a so-called partial ROM medium. In the ROM portion, information is recorded by physical change such as an irregularity formed as, for example, pits. In the RAM portion, a recording layer that allows writing or overwriting is formed. In the partial ROM medium, the ROM portion and the RAM portion are formed on separate regions of a single disk.
In such a medium having both ROM portion and RAM portion on a single optical disk, synchronization flags for establishing synchronization between signals reproduced from the ROM portion and the RAM portion are embedded in data recorded in the ROM portion and the RAM portion of the optical disk. When reproducing data, the synchronization flags are recognized by a read channel and data reproduced from the ROM portion and the RAM portion are combined again to perform reproduction.
However, as mentioned above, in a partial ROM medium, a ROM portion and a RAM portion are formed on separate regions of a single optical disk. Accordingly, in such a system that reproduces data recorded in the ROM portion and the RAM portion, and combines and uses the data, it is necessary to access the ROM portion and the RAM portion by an optical pickup and reproduce data from each of the regions. Thus, it is necessary for the optical pickup to constantly move between and access the ROM portion and the RAM portion. Hence, there is a significant time delay until data reproduced from the ROM portion and the RAM portion and to be synchronized are sent from the optical pickup to the read channel. Consequently, reliability of the reproduced data has been low.
Additionally, in a rewritable medium, access history of regions to be accessed and user information such as kinds of registration information are written and recorded in control tracks. However, since it is impossible to secure a large capacity for the control tracks, the amount of information that can be written therein has been limited.
On the other hand, in a so-called concurrent ROM-RAM medium, which includes a ROM portion having an optically transparent substrate on which information is recorded by physical change such as an irregularity, and a RAM portion formed on the ROM portion as a recording layer and allowing writing at least once, it is possible to concurrently handle data of the ROM portion and the RAM portion.
As for concurrent ROM-RAM media, a concurrent ROM-RAM optical disk that allows simultaneous reproduction of the ROM portion and the RAM portion is described in, for example, an article titled “Feasibility Study of Concurrent ROM-RAM Optical Disk” in The Journal of the Institute of Television Engineers of Japan, Vol. 46, No. 10, pp. 1319–1324, published in 1992.
However, in order to concurrently handle data of the ROM portion and that of the RAM portion, it is necessary to recognize relationships between the data recorded in the ROM portion and that in the RAM portion with a simple method.
Additionally, in a concurrent ROM-RAM medium, general contents such as a movie and music are recorded in the ROM portion, and in many cases, the recorded contents are used by multiple users. Hence, in terms of data protection and copyright protection, methods are required for managing access history and the like, recording user information such as various kinds of registration information, and identifying users who desire to use the concurrent ROM-RAM medium. It is necessary that such methods can be performed as simply as possible.